Ultra high vacuum handling equipment such as that used in semiconductor processing and other ultra high vacuum environments typically have valves appropriately located therein to control flow of gases through the equipment. Such ultra high vacuum equipment valves can have a variety of different configurations but are often configured as poppet valves which can be actuated in a variety of different ways to provide access between an inlet and an outlet of the valve.
Often a pressure of the gases on either side of the valve are somewhat different before the valve is opened. When the valve is initially opened a rush of gas through the valve occurs to equalize pressure on either side of the valve. This rush of air to equalize pressure through the valve can be undesirable in many circumstances. For instance, in semiconductor device manufacturing equipment, it is important that contaminants be eliminated from regions where manufacturing processes are occurring. When a rush of air occurs through a valve that is opening, particles which had previously settled to inside surfaces of the vacuum handling equipment can be stirred up into a free floating state and then land on devices being processed, causing damage.
One known technique for eliminating an initial rush of air through an opening valve and the related negative consequences is to utilize a valve having a "soft start" feature. Soft start valves include two ports/pathways passing between a single common inlet of the valve and a single common outlet of the valve. The first soft start port is significantly smaller in size than a second "main" port. When the valve is to be opened, the soft start port is opened first so that pressure can be equalized through a small soft start passage. This smaller passage is sufficiently small that pressure is balanced between the inlet and the outlet of the valve without stirring up particulates which may be resting on either side of the valve. After pressure has been equalized through the soft start passage, the main port is opened to provide full communication between the inlet and the outlet of the valve.
Known prior art valves which include such a soft start feature include the "Series 62" angle valve with soft start function provided by VAT, Inc. of Woburn, Mass.; the "VacuComp" series 150/160 valve by MKS Instruments, Inc. of Boulder Colo.; and the "XLD" vacuum soft start valves by SMC Pneumatics, Inc. of Indianapolis, Ind. While these known prior art "soft start" valves are generally effective, they suffer from being unnecessarily complex and including substantially separate activation systems for the two ports, resulting in valves which are difficult to manufacture and which are not as easily maintained in proper working order. Such drawbacks are particularly magnified in semiconductor processing equipment where automated processes require repetitive opening and closing of the valves over long periods of time.
Accordingly, a need exists for a "soft start" valve which has a simpler design and which has fewer moving parts so that a valve capable of longer life, greater reliability and simpler manufacture is provided.